Fastest I've stepped off a plane at EZE to exiting the terminal has been less than half an hour but we always order our taxi pick up one hour after the scheduled arrival time especially during peak times. Much depends on how many other arrivals there are as to how long it will take you to get through immigration and customs.
Traffic will be heading into the city at that time of day which might lead to delays but all going well the road journey should take around 45 minutes. I personally would feel more comfortable with a four hour minimum connection time.